Ukrainian soldier stand behind a fence while unidentified armed men block the headquarters of the Ukrainian Navy in Sevastopol on March 3, 2014. The Russian Black Sea Fleet commander Aleksandr Vitko has issued an ultimatum to the Ukrainian military personnel in Crimea, the Interfax-Ukraine news agency reported. Ukraine accused Russia on Monday of pouring more troops into Crimea as world leaders grappled with Europe's worst standoff since the Cold War and the Moscow market plunged on fears of an all-out conflict. AFP PHOTO/ VIKTOR DRACHEV (Photo credit should read VIKTOR DRACHEV/AFP/Getty Images)

A Ukrainian soldier stands behind a fence while unidentified armed men block the headquarters of the Ukrainian Navy in Sevastopol on March 3, 2014. (credit: VIKTOR DRACHEV/AFP/Getty Images)

WASHINGTON (CBSDC/AP) — Russia is calling on Ukrainian forces in Crimea to surrender by Tuesday morning.

Reuters reports that Russia’s Black Sea Fleet Commander Alexander Vitko warned that Ukraine will face a “military assault” if they don’t surrender by 5 a.m. Tuesday. The Associated Press reports that Russia wants Ukraine to surrender two warships in Crimea.

“If they do not surrender before 5 a.m. tomorrow, a real assault will be started against units and division of the armed forces across Crimea,” a Ukraine Defense Ministry source reportedly said.

A Russian government source has denied that they have told Ukraine forces to surrender in Crimea.

On the ground, pro-Russian troops held all Ukrainian border posts Monday in Crimea, as well as all military facilities and a key ferry terminal, cementing their stranglehold on the strategic Ukrainian peninsula.

“This is a question of defending our citizens and compatriots, ensuring human rights, especially the right to life,” Russian Foreign Minister Sergey Lavrov said in Geneva, where he was attending U.N. meetings.

There have been no reports, however, of any hostilities toward Russian-speakers in Ukraine during the country’s four months of political upheaval.

Tension between Ukraine and Moscow rose sharply after fugitive President Viktor Yanukovych was pushed out by a protest movement made up of people who wanted closer ties with the European Union, more democracy and less corruption. Yanukovych fled to Russia last month after more than 80 demonstrators were killed – mostly by police – near Kiev’s central square but insists he is still president.

In Kiev, Ukraine’s new prime minister admitted his country had “no military options on the table” to reverse Russia’s military move into its Crimea region, where Ukraine’s military admitted that pro-Russian troops have surrounded or taken over “practically all” its military facilities.

While Prime Minister Arseniy Yatsenyuk appealed Monday for outside help and insisted that Crimea still remained part of his country, European foreign ministers held an emergency meeting on a joint response to Russia’s military move that could include economic sanctions. But there was no immediate response to the Russian statement, which would void the new government that Ukraine installed just last week.

“Any attempt of Russia to grab Crimea will have no success at all. Give us some time,” Yatsenyuk said at a news conference with British Foreign Secretary William Hague in Kiev.

But he added that “for today” there were “no military options on the table.” He said his country was “urgently” asking for economic and political support from other countries.

“Crisis diplomacy is not a weakness, but it is now more important than ever for us not to fall into the abyss of a military escalation,” German Foreign Minister Frank-Walter Steinmeier said in Brussels.

In the meantime, Russian forces were clearly in charge in Crimea, home to 2 million mostly Russian-speaking people and landlord for Russia’s critical Black Sea Fleet at Sevastopol.

In addition to seizing barracks and border posts, troops also controlled a ferry terminal in the Ukrainian city of Kerch, just 20 kilometers (12 miles) across the water from Russia. That intensified fears in Kiev that Moscow will send even more troops into the peninsula via that route.

The soldiers at the terminal refused to identify themselves Monday, but they spoke Russian and their vehicles had Russian license plates.

Border guard spokesman Sergei Astakhov said the Russians were demanding that Ukrainian soldiers and guards transfer their allegiance to Crimea’s new pro-Russian local government.

“The Russians are behaving very aggressively, they came in by breaking down doors, knocking out windows, cutting off every communication,” he said.

He said four Russian military ships, 13 helicopters and 8 transport planes had arrived in Crimea in violation of agreements that permit Russian to keep its naval base at Sevastopol.

Now, fears in the Ukrainian capital of Kiev and beyond are that Russia might seek to expand its control by targeting and seizing other parts of Ukraine, especially in its pro-Russian east.

“The world cannot just allow this to happen,” Hague said, but he ruled out any military action. “The U.K is not discussing military options. Our concentration is on diplomatic and economic pressure.”

Outrage over Russia’s military moves has mounted in world capitals, with U.S. Secretary of State John Kerry calling on Russian President Vladimir Putin to pull back from “an incredible act of aggression.” Kerry is to travel to Ukraine on Tuesday.

Putin has rejected calls from the West, insisting that Russia has a right to protect its interests and those of Russian-speakers anywhere in Ukraine. His confidence is matched by the knowledge that Ukraine’s 46 million people have divided loyalties – while much of western Ukraine wants closer ties with the 28-nation European Union, its eastern and southern regions like Crimea look to Russia for support and trade.

Faced with the Russian threat, Ukraine’s new government has moved to consolidate its authority, naming new regional governors in the pro-Russia east, enlisting the support of the country’s wealthy businessmen and dismissing the head of the country’s navy after he declared allegiance to the pro-Russian government in Crimea.

NATO held an emergency meeting in Brussels and the U.S., France and Britain debated the possibility of boycotting the next Group of Eight economic summit, to be held in June in Sochi, the host of Russia’s successful Winter Olympics.